Electronic devices, such as optoelectronic devices, can be fabricated using organic materials, particularly using thin-film processing techniques. Such organic optoelectronic devices can be volumetrically compact because of their relatively thin and planar structure, along with providing enhanced power efficiency and enhanced visual performance, such as compared to other display technologies. In certain examples, such devices can be mechanically flexible (e.g., foldable or bendable), or optically transparent, unlike competing technologies. Applications for an organic optoelectronic device can include general illumination, use as a backlight illumination source, or use as a pixel light source or other element in an electroluminescent display, for example. One class of organic optoelectronic devices includes organic light emitting diode (OLED) devices, which can generate light using electroluminescent emissive organic materials such as small molecules, polymers, fluorescent, or phosphorescent materials, for example.
In one approach, OLED devices can be fabricated in part via vacuum deposition of a series of organic thin films onto a substrate using the technique of thermal evaporation. However, vacuum processing in this manner is relatively: (1) complex, generally involving a large vacuum chamber and pumping subsystem to maintain such vacuum; (2) wasteful of the organic raw material, as a large fraction of the material in such a system is generally deposited onto the walls and fixtures of the interior, such that more material is generally wasted than deposited onto the substrate; and (3) difficult to maintain, due to the need to frequently stop the operation of the vacuum deposition tool to open and clean the walls and fixtures of the built up waste material. Furthermore, in most OLED applications it is desirable to deposit the organic films in a pattern.
In one approach, a blanket coating can be deposited over the substrate and photolithography could be considered for achieving the desired patterning. But in many applications and for most OLED materials in particular, such photolithography processes can damage the deposited organic film or the underlying organic films. A so-called shadowmask can be used to pattern the deposited layer directly when utilizing the vacuum deposition method. The shadowmask in such cases comprises a physical stencil, often manufactured as a metal sheet with cut-outs for the deposition regions. The shadowmask is generally placed in proximity to or in contact with, and aligned to, the substrate prior to deposition, kept in place during deposition, and then removed after deposition. Such direct-patterning via shadowmask adds substantial complexity to vacuum-based deposition techniques, generally involving additional mechanisms and fixturing to handle and position the mask precisely relative to the substrate, further increasing the material waste (due to the waste from material deposited onto the shadowmask), and further increasing the need for maintenance to continuously clean and replace the shadowmasks themselves. Shadowmask techniques also generally involve relatively thin masks to achieve the pixel scale patterning required for display applications, and such thin masks are mechanically unstable over large areas, limiting the maximum size of substrate that can be processed. Improving scalability remains a major challenge for OLED manufacturing, so such limitations on scalability can be significant.
The organic materials used in OLED devices are also generally highly sensitive to exposure to various ambient materials, such as oxygen, ozone, or water. For example, organic materials used in various internal layers of an OLED device, such as including an electron injection or transport layer, a hole injection or transport layer, a blocking layer, or an emission layer, for example, can be subject to a variety of degradation mechanisms. Such degradation can be driven at least in part by incorporation of chemically or electrically/optically active contaminants into the device structure, either within the bulk material of each film or at the interfaces between layers in the overall device stack. Over time chemically active contaminants can trigger a chemical reaction in the film that degrades the film material. Such chemical reactions can occur simply as a function of time, absent any other triggers, or can be triggered by ambient optical energy or injected electrical energy, for example. Electrically/optically active contaminants can create parasitic electrical/optical pathways for the electrical/optical energy introduced or generated in the device during operation, and such pathways can result in suppression of light output, or generation of incorrect light output (e.g., light output of the wrong spectrum.) The degradation or loss may manifest as failure of an individual OLED display elements, “black” spotting in portions of an array of OLED elements, visible artifacts or “mura,” loss of electrical/optical efficiency, or unwanted deviation in color rendering accuracy, contrast, or brightness in various affected regions of the array of OLED elements.